Oil and gas reservoirs are produced by drilling wells of vertical, deviated or horizontal orientation, cementing and perforating the casing, installing tubing and connecting the tubing to a pipeline. In many formations, large increases in productivity can be achieved by stimulating production through reduction of local flow resistance near the well. In particular, hydraulic fracture stimulation involves pumping high pressure fluids (water and propant) into the formation through the casing perforations to fracture the rock and thereby lead to high conductivity paths for the oil and gas to flow along into the well. As oil and gas become increasingly hard to find, are produced from less economical formations, and with the high cost of creating hydraulic fractures, it is imperative for operators to predict the performance of these fractures for both horizontal and vertical wells. It is very difficult to know the extent of fractures and their productivity, since seismic data is quite inaccurate at the depths typically incurred today.
In the existing operating environment, making quick decisions about hydraulic fracture design (i.e. size of job, pounds of sand to pump, type of sand, etc.) is a necessity. Especially in low permeability rock, fracture quality and design are critical to success on these projects. The value of planning in areas of prospect identification, field development, and facilities design has been well documented. The value of planning and optimization for completion design is no different. However, planning based on quantitative modeling is rarely done at this stage. How is the desired half length determined? Although it should be based on optimized production per unit of cost, fracture design is based primarily on the last job done in the area of interest.
Due to the extreme importance of a well-performing hydraulic fracture, recent industry efforts have been focused on trying to model hydraulic fractures. However, the majority of this effort has been accomplished using traditional reservoir simulators with some form of local grid refinement. This grid refinement exercise is done because industry experts recognize the importance of capturing the most resolute picture of fluid flow around the hydraulic fracture as possible. Unfortunately, this grid refinement, by and large, takes a significant amount of time and expertise due to the tools available. Furthermore, the resolution is still not fine enough. In addition, it does not allow the time needed to perform an analysis for common operational environments that exist in low perm areas. Analysis using existing simulators cannot be executed quickly enough to be able to be inserted into the process of well stimulation design and drilling optimization plans.
There is no doubt that the process of finding (acreage position, data acquisition, seismic interpretation, mapping, drilling locations, economics and risk analysis) and developing (exploratory drilling, facilities, infill drilling) oil and gas properties is expensive. Understanding how a hydraulic fracture improves production performance is important to enable optimal completion and field development strategy. To truly understand fracture performance, understanding of reservoir performance is a must.